Observation of variations with time of a nuclear magnetic resonance (NMR) image is important for an increasing number of clinical applications. For example, variation in time of contrastant intake is important for diagnosis of tumors as well as for perfusion studies. Also, by way of example, electrocardiogram dependent signal variations are used for characterizing processes which vary with the cycle of the heart.
A problem in observation of variations in time is the intrinsically low time resolution of image-producing NMR-tomography methods. Prior to the present invention, this problem was at least partially avoided by using extremely short measuring sequences. Methods used in this connection include echo planar imaging (described by Mansfield in J. Phys. C, 10, L55 (1977)) and very fast gradient echo sequences (described in A. Haase, Magn. Res. Med. 10, 135 (1989)). These methods are sufficiently fast only by using particular fast and strong magnetic field gradients. Image-recording times of less than 300 ms cannot be achieved with commonplace apparatus in this manner. In addition, the inherent short recording sequences often do not offer the image contrast which is relevant for the intended application.